Internal combustion engine pistons typically have several rings positioned in respective circumferential grooves proximate the closed (domed) end of the piston. For example, a typical internal combustion engine piston will include an inner expander ring with so-called rail rings on opposite sides thereof in the same groove, an intermediate cast iron compression ring, and outer cast iron or steel compression ring proximate the closed (domed) end of the piston.
The compression rings typically are made of cast iron or steel and precision ground so as to be nearly perfectly flat and thus resistant (stiff) to bending out of a flat profile. Compression rings can be from 3 mm to 1 mm in thickness and have square or radiused inner diameters.
Expander rings, on the other hand, typically are made of stainless steel and include vertical and/or horizontal corrugations. Expander rings are relatively flimsy and easily bendable out of a flat profile as compared to compression rings during the assembly operation into the respective piston grooves. Expander rings can be from 5 mm to 2 mm in thickness.
Each corrugated expander ring typically is bounded or supported on each side in the same piston groove by what are called rail rings which are much thinner, spring steel rings. For example, the rail rings can typically have a thickness of 0.3 mm to 0.8 mm. The rail rings are adapted to wipe the cylinder wall of the internal combustion engine in a manner to provide a controllable thin oil lubricating layer thereon. As a result of their thinness and spring steel properties, the rail rings are prone to "oil-can" when radially expanded during assembly into the piston groove on opposite sides of the expander ring. "Oil canning" is a bowing of the thin rings into a two cycle wave (sinusoidal wave) type configuration when radially expanded during the ring-piston groove assembly operation.
This "oil canning" makes assembly of the thin rail rings onto the piston groove difficult and unreliable.
There is a need for piston ringing apparatus that can be used to assemble thin rail and similar rings onto internal combustion engine pistons at one or more piston ringing stations under high volume production conditions in a manner to avoid "oil canning" of the rings such that the rate and reliability of ring assembly on the pistons is much improved.
There also is a need for piston ringing apparatus that can be used to assemble thin rail and similar rings onto internal combustion engine pistons at one or more piston ringing stations and that can be further automated in a manner that improves the assembly rate and reliability of ring/piston assembly.
It is an object of the invention to satisfy these needs.